The energy-dependent movement of molecules within the plane of the plasma membrane is a widespread but poorly understood phenomenon of considerable significance to cell biology. Cellular redistribution of surface molecules plays a role in endocytosis, membrane turnover, activation of lymphocytes and down regulation of cell surface receptors; this process may also be involved in certain forms of whole cell locomotion. Defects in the ability of the cell to regulate the distribution of components in the plane of the plasma membrane are associated with malignant transformation of cells in addition to a number of other clinical conditions, such as familial hypercholesterolemia. The Chlamydomonas flagellum provides a useful experimental system in which to study this class of dynamic plasma membrane phenomena using a judicious combination of immunological, genetic and morphological approaches. A recently isolated and characterized panel of mouse monoclonal antibodies to carbohydrate and protein epitopes on flagellar membrane proteins, glycoproteins and glycolipids will be utilized to probe the mechanism underlying flagellar surface motility. Specifically, these reagents will be utilized for purification of flagellar membrane components, determination of the distribution of these components, as a means to directly visualize redistribution and as probes to interfere with flagellar membrane function. Those monoclonal antibodies that recognize flagellar surface-exposed epitopes will be utilized to select for mutant cell strains defective in particular flagellar membrane components using fluorescent-activated cell sorting and whole cell immunoaffinity chromatography. Characterization of these mutant cell strains, along with the characterization of mutant cell strains already available in the laboratory that are defective in flagellar surface motility, should allow a clearer understanding of the machinery involved in generating force at the cell surface for lateral translocation of plasma membrane components.